Large-scale smelting in the Mansfeld Kupferschiefer mining district began during the late 19^th century with the introduction of shaft furnaces in the metallurgical complexes at Eisleben and He/bra. Flue gas treatment from 1904 onward provided considerable amounts of metalliferous sludge (Theisen-sludge) which contained up to 18% Zn, 14% Pb, 1.2% Cu and 1.2% Sn. After metal recovery from this sludge ceased in 1978, more than 300,000 metric tons of "waste" were deposited in open basins on extensive heaps of slag and mining debris.

At the He/bra smelting complex, suspended Theisen-sludge (grain-size < 1 μm) has infiltrated the fractured slag heaps and currently contributes both heavy-metal particles and leachate to ground and surface water pollution; seepage waters contain up to 2.5 g/l Zn. In addition to water pollution, the extremely fine-grained Theisen-sludge is scattered by the wind from its uncovered storage sites and causes additional environmental hazards.

Detailed studies into the potential heavy-metal leaching from Theisen-sludge, slag, Kupferschiefer ore and carbonaceous host rocks indicate that dissolution and wind-borne dispersion of Theisen-sludge are the main Zn migration mechanisms into the surrounding environment. Very high Zn contents were released during Theisen-sludge leaching experiments using both the heap materials and adjacent soils, and testing each under laboratory as well as natural climatic conditions. The high Zn mobilization rate is due to ionic dissolution under natural pH-Eh conditions. In contrast, Pb and Cu form stable secondary minerals (carbonates and sulfates) under the same test conditions, resulting in very low dissolved abundances (ppm levels) from the same source material. Tests of low-grade Kupferschiefer ore found that Zn, Cu and Pb were all below 5.0 ppm in solution. Soil profiles located close to the slag heaps show metal enrichment patterns in the topsoil that are identical to those of Theisen-sludge, which is consistent with wind dispersion of Theisen-sludge.